As part of the new Windows 10 for Phone, Microsoft is making sure that it includes the latest and greatest in Bluetooth Hands-Free Profiles for improved sound and voice quality. As part of the wide range of announcements they made last week at WinHEC in China, Microsoft announced that the new mobile platform will support the Hands-Free Profile (HFP) standard 1.6 which requires, amongst other things, the support for high definition audio. Microsoft is referring to this as Wideband speech but you may also know if it as HD Voice and it should significantly improve the audio quality of calls and using voice activated services like Cortana on the new platform.
Currently in Windows Phone 8.1, only narrowband audio is only support which can lead to voice quality issues on calls and can lead to voice activated service not understanding your commands.
The new HFP standard is aimed squarely at eliminating these challenges and users should see a significant improvement in Windows 10 for Phone. In addition to this, the new platform will continue to support the aptX audio codec, something that can be found in Lumia Denim today. This allows you to have wired-level sound quality on Bluetooth A2DP and minimizes latency as well as improves audio/video sync issues.
The motivation for Microsoft to improve audio quality out of Bluetooth is clear in that they want to make sure you can use things like Cortana while in a hands-free mode (something that is required while operating a vehicle in many US states, the UK and part of Europe) but also make sure that audio quality for the user and the receiver of the calls are crisp as well. To take full advantage of this you will need to make sure your Bluetooth headset supports HFP 1.6 which most of the mid-to-high end devices already support.